PRIESTLEY. iat 
PRESIDENTIAL ADDRESS 
but he was the originator of the whole work. For when 
I had shown him: that I had discovered the nature of the 
motion of the celestial bodies he never ceased to ask me to 
communicate it to the Royal Society; till at last he 
succeeded by his importunity and kindly encouragement 
in making me think of publication.”’ 
We know from other sources that Halley bore a large 
part of the cost of publication and dropped his own 
researches for a year or two in order to keep Newton up 
to the mark and push the great work through the press. 
The world owes much to the genius of Newton, but it owes 
no less to the perseverance, generosity, and self-sacrifice 
of Halley. 
Two facts stand out in the above outline of the 
development of scientific thought: the sterility of medieval 
science under a weight of metaphysical speculation, and 
the fertility restored by a return to experience which in 
less than a century produced the Principia. In view of 
these facts it was natural that subsequent developments 
should be characterized by a distrust of metaphysics. In 
the light of recent research, however, it appears that a 
wrong attitude to metaphysical questions may again lead 
to the stagnation of-scientifie work. We noticed, earlier 
in the evening, that one difference between ancient and 
modern science is the difference of aim; the old search 
after first causes has been replaced by attempts to formulate 
ordered descriptions. We no jonger aecept Newton’s rule 
and reason that ‘‘no more causes are to be admitted than 
_are sufficient to explain the phenomena, because, as the 
philosophers say, Nature does nothing in vain and it is 
vain to use many means when few will suffice. Nature is 
simple and does not run riot with superfluous causes.”’ 
Rather do we accept the dictum of the French philosopher 
who said that Nature pays no heed to the difficulties of 
analysis, while at the same time we attempt to summarize 
our description of Nature in as few and as general state- 
ments as possible. Since our aim is description we are not 
concerned with the metaphysical problem of reality. The 
Newtonian scheme of Space and Time forms an adequate 
framework for the Newtonian Mechanics in terms of which 
has been built up a system of Natural Philosophy that has 
served us for two hundred years; the question of the 
